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. 2024 Oct 22;10(21):e39702.
doi: 10.1016/j.heliyon.2024.e39702. eCollection 2024 Nov 15.

IAA-producing bacteria from the rhizosphere of chickpea (Cicer arietinum L.): Isolation, characterization, and their effects on plant growth performance

Debebe Landina Lata  1 , Oumer Abdie  1 , Yayis Rezene  2
Affiliations

IAA-producing bacteria from the rhizosphere of chickpea (Cicer arietinum L.): Isolation, characterization, and their effects on plant growth performance

Debebe Landina Lata et al. Heliyon. .

Abstract

Indole-3-acetic acid (IAA), a crucial plant hormone, regulates diverse physiological processes. This study aimed to isolate and characterize IAA-producing bacteria from the chickpea (Cicer arietinum L.) rhizosphere and evaluate their effects on plant growth. From 54 rhizosphere samples, 118 bacteria (designated as GAC) were isolated and screened for IAA production using a Salkowski colorimetric assay, and Bergey's manual was used for biochemical identification. Isolates were grown under various conditions and in vitro screened for their growth promotion traits. A PCR investigation was performed for IAA and nitrogen-fixing genes, and evaluated for greenhouse conditions. Among them, 27 isolates produced IAA, with eight high producers selected. Morphological and biochemical identification classified the six isolates as Pseudomonas and the other two as Bacillus. Optimal conditions for IAA production were observed at 500 μg/ml tryptophan, 35 °C, and pH 7.0. A 48-h incubation was ideal for IAA production, except for GAC-34 and GAC-73, which required 72 h. All the isolates achieved optimal IAA levels with tryptone and sucrose as nitrogen and carbon sources, respectively. Moreover, all isolates showed nitrogen fixation ability, and the six isolates exhibited phosphate solubilization. PCR confirmed the amplification of nifH (300 bp), nifK (360 bp), and ipdC (1170 bp) genes. Greenhouse experiments demonstrated that eight selected isolates significantly enhanced chickpea growth parameters (p < 0.001). These findings suggest that these IAA-producing bacteria have the potential to be used as biofertilizers to improve crop productivity, although further molecular identification and field studies are required.

Keywords: Bio-inoculants; Chickpea; Indole-3-acetic acid; Molecular analysis; PGPR; Rhizosphere.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper:Debebe Landina Lata reports financial support was provided by wolkite University, Department of Biotechnology. Debebe Landina Lata reports a relationship with 10.13039/501100022540Wolkite University that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image 1
Graphical abstract
Fig. 1
Fig. 1
Map of chickpea rhizosphere samples collection sites/area.
Fig. 2
Fig. 2
IAA production by bacterial isolates; (A): pink color positive result and (B): yellow color negative result.
Fig. 3
Fig. 3
IAA production by bacteria isolates from chickpea rhizosphere samples.
Fig. 4
Fig. 4
Morphological and biochemical characterization of bacterial isolates. (A): gram-positive isolate; (B): gram-negative isolate; (C): GAC-118 isolate on Kings B-medium; (D): positive motility test; (E): positive methyl red test; (F): positive triple sugar iron test; (G): positive citrate utilization; and (H): negative Vogues-Proskauer's test.
Fig. 5
Fig. 5
Effect of different L-tryptophan concentrations on IAA production by bacterial isolates (means (n = 3) ± standard deviation).
Fig. 6
Fig. 6
The effect of the incubation periods on IAA production by bacterial isolates (means (n = 3) ± standard deviation).
Fig. 7
Fig. 7
The effect of the different pH values on IAA production by bacteria (means (n = 3) ± standard deviation).
Fig. 8
Fig. 8
The effect of different temperatures values on IAA production by bacterial isolates (means (n = 3) ± standard deviation).
Fig. 9
Fig. 9
The effect of carbon sources concentration on IAA production by bacterial isolates (means (n = 3) ± standard deviation).
Fig. 10
Fig. 10
The effect of nitrogen sources concentration on IAA production by bacterial isolates (means (n = 3) ± standard deviation).
Fig. 11
Fig. 11
Gel electrophoresis of ipdC (1170 bp) gene amplified by PCR. Lane name with respective isolates; M-(100 bp ladder), 2–(GAC-2), 34-(GAC-34), 117-(GAC-117), 73-(GAC-73), 91-(GAC-91), 92-(GAC-92), 7-(GAC-7), 22-(GAC-22), 118-(GAC-118), 12-(GAC-12), 61-(GAC-61), 30-(GAC-30), 42-(GAC-42), 43-(GAC-43), 44-(GAC-44), 58-(GAC-58), 59-(GAC-59), 82-(GAC-82), 88-(GAC-88), 90-(GAC-90), 104-(GAC-104), 24-(GAC-24), 106-(GAC-106), and 108-(GAC-108).
Fig. 12
Fig. 12
Gel electrophoresis of nifK (360 bp) gene amplified by PCR. Lane name with respective isolates; M-(100 bp ladder), 2–(GAC-2), 34-(GAC-34), 117-(GAC-117), 73-(GAC-73), 92-(GAC-92), 91-(GAC-91), 7-(GAC-7), 22-(GAC-22), 118-(GAC-118), 12-(GAC-12), 61-(GAC-61), 30-(GAC-30), 42-(GAC-42), 43-(GAC-43), 44-(GAC-44), 58-(GAC-58), 59-(GAC-59), 82-(GAC-82), 88-(GAC-88), 90-(GAC-90), 104-(GAC-104), 105-(GAC-105), 106-(GAC-106), and 108-(GAC-108).
Fig. 13
Fig. 13
Plant growth promoting potential of IAA-producing isolates in pot experiment.
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